1. Field of the Invention
The present invention relates to the field of display technology, and in particular to a method for manufacturing a polymer dispersed liquid crystal (PDLC) display device and a PDLC display device.
2. The Related Arts
A thin-film transistor liquid crystal display (TFT-LCD) generally comprises a color filter (CF) substrate and a thin-film transistor (TFT) substrate. The substrates have inside surfaces facing each other and comprising transparent electrodes provided thereon. A layer of liquid crystal is interposed between the two substrates. The liquid crystal display controls the orientation of liquid crystal molecules through application of an electric field in order to change the state of polarization of light and selectively blocks or passes a light path by means of polarizers so as to achieve the purpose of displaying.
It can be said that for almost all sizes of display devices, including large, medium, and small sizes, the LCDs take an absolutely predominant share of the market. In today's LCD market of applications, an increasing demand is emerging for terminal displays used in large shopping malls, supermarkets, hotel lobbies, theaters and cinemas, education, medication, and other public sites where people crowd and the yearly increasing rate is 30%.
On the other hand, polymer dispersed liquid crystal (PDLC), serving as a liquid crystal light regulation valve, has been paid close attention to and widely used in recent years and is a material that is formed by mixing low molecule liquid crystal and pre-polymer to generate a polymerization reaction under certain conditions so as to form micrometer-size liquid crystal droplets uniformly dispersed in a high-molecule polymer network and exhibits characteristics of electro-optic response by means of anisotropic dielectric property of the liquid crystal molecules for being operable between a scattering state and a transmission state and demonstrating a predetermined grey level. A PDLC display device offers various advantages, such as omitting the use of polarizers and alignment layers, being easy to manufacture, being easy to make a large-sized flexible display device, and has been widely used in optic modulators, thermal-sensitive and pressure-sensitive devices, electrically-controlled glass, light valves, projection displaying, and electronic books. The operation principle is that no regular electric field can be established between films without an external voltage applied and optic axes of liquid crystal droplets are oriented stochastically, demonstrating a disorderly condition, so that effective refractive index n0 does not match refractive index np of the polymer. Incident light would be strongly scattered so that the film shows an opaque or translucent condition. When an external voltage is applied, the optical axes of the liquid crystal drops are aligned in a direction normal to a surface of the film, meaning being consistent with the direction of the electric field. Ordinary refractive index of the droplets and the refractive index of the polymer generally match each other so that there is no apparent interface therebetween thereby forming a generally homogeneous medium, and thus, no scattering will happen to incident light and the film demonstrates a transparent condition. Thus, in a condition of being driven by an external electric field, PDLC exhibits the characteristics of being a light switch and the degree of transparency is increased according to a predetermined curve when the applied voltage is increased.
In addition, quantum dots, as a newly emerging material for display devices, have been widely accepted and paid close attention to. Quantum dots are a quasi-zero-dimensional nanometer-sized material and are generally formed of a small amount of atoms. Roughly speaking, a quantum dot has a size that is less than 100 nm in each of the three dimensions and shows an external appearance as an extremely small dot-like article with movement of an internal electron thereof being confined in each direction so as to exhibit a significant quantum confinement effect. The quantum dot shows an excitation spectrum that is wide and distributed continuously and an emission spectrum that is narrow and symmetric, providing various advantages, including color controllability, high photochemistry stability, and extended fluorescent life time, thereby making it an ideal luminescent material. Currently, quantum dots are classified as two types according to the ways of energy acquisition, one being photoluminescence and the other electroluminescence. The color of light emitting from a quantum dot is achieved with the size effect of the quantum dot, namely controlling the shape, structure, and size of the quantum dot to control the electron states of energy band gap, magnitude of exciton bonding energy, and exciton energy blue shifting.
Further, graphene has also started to play a role of application in TFT-LCDs and is an important milestone scientific discovery in the field after fullerenes and carbon nanotubes. Graphene is a two-dimensional crystal composed of a single carbon layer formed of carbon atom connected though sp hybridization, having a basic structure unit comprising benzene six-member ring that is the most stable structure of the organic materials. An electron, when moving in the orbit of graphene, does not undergo scattering caused by lattice defects or foreign atoms. Due to the presence of π-orbit in the plane of the graphene sheet, electrons are allowed to move freely in the crystal so that the graphene possesses excellent electron transportation characteristics. It also shows various unique properties, such as zero energy gap, extraordinary quantum Hall effect, and Landau quantum behavior, so as to increasingly attract the attention of people involved in the flat panel display industry for research and study of the application thereof.